Implement CSS: scroll-boundary-behavior

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index a67d5daa6b6ed92a786f29761a9469fa43a62f88..0267527bf1062e8b0b37eb8074e659c46a13fad4 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -77,6 +77,7 @@
 #include "platform/graphics/paint/PaintRecordBuilder.h"
 #include "platform/graphics/paint/TransformDisplayItem.h"
 #include "public/platform/WebLayerStickyPositionConstraint.h"
+#include "public/platform/WebScrollBoundaryBehavior.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/text/StringBuilder.h"
 
@@ -1080,11 +1081,21 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry(
   updateShouldFlattenTransform();
   updateChildrenTransform();
   updateScrollParent(scrollParent());
+  updateScrollBoundaryBehavior();

[bokan, 2017/03/23 13:18:26]

Hmm...I'm not sure CLM::updateGraphicsLayerGeometry will get called if you just
change the scrollBoundaryBehavior. Do you know how that happens? If not, I think
you'll need to add a call to CLM::setNeedsGraphicsLayerUpdate. This gets called
when the scroll offset is changed so it might work in most cases but we should
probably do it explicitly when the CSS value changes. Is there another CSS
feature that needs to communicate behavior to the compositor like this so we can
reuse its path?

[sunyunjia, 2017/03/23 20:16:54]

I checked the call stack, and found both CLM::updateGraphicsLayerGeometry and
CLM::setNeedsGraphicsLayerUpdate are called from
FrameView::updateAllLifecyclePhases

   registerScrollingLayers();
 
   updateCompositingReasons();
 }
 
+void CompositedLayerMapping::updateScrollBoundaryBehavior() {
+  ScrollBoundaryBehavior behavior =
+      layoutObject().styleRef().getScrollBoundaryBehavior();
+  if (m_scrollingContentsLayer) {
+    m_scrollingContentsLayer->setScrollBoundaryBehavior(
+        static_cast<WebScrollBoundaryBehavior>(behavior));
+  }
+}
+
 void CompositedLayerMapping::updateMainGraphicsLayerGeometry(
     const IntRect& relativeCompositingBounds,
     const IntRect& localCompositingBounds,